1. Technical Field
The present invention relates to a technique for preventing a reduction in touch detection accuracy due to noise generated in a display panel.
2. Related Art
In display panels using liquid crystal, a liquid crystal capacitor constructed by interposing liquid crystal between a pixel electrode and a common electrode (counter electrode) is arranged so as to correspond to each of the intersections of scanning lines and data lines. A voltage according to a gray scale (brightness) is written into each liquid crystal capacitor to perform predetermined display. In recent years, some of the above-described display panels have included a touch panel for detecting a touched state (hereinafter, also referred to as “touch detection”). In the case where a touch panel is provided for a display panel, an image according to an input on the touch panel can be displayed on the display panel. Accordingly, the convenience of users can be improved.
Disadvantageously, the display panel is a source of generating various noises. The noises propagate to the touch panel and adversely affect touch detection. JP-A-10-124233 discloses a technique for dividing a period of one frame (generally, 16.7 ms) in the display panel into a writing period for display and a detecting period, and performing touch detection on a touch panel in the detecting period to prevent noise generated during the writing period from affecting touch detection on the touch panel.
According to this technique, however, touch detection is largely constrained because the detection on the touch panel is limited to once every frame. Recently, in order to suppress voltage swings in the data lines during AC driving of the liquid crystal capacitors, a voltage across the common electrode has been alternately switched between a low voltage and a high voltage. Unfortunately, an influence of noise associated with switching of the voltage across the common electrode is not negligible.